1. Field of the Invention
The invention relates to transparent, low-migration organic silicone copolymers of defined melt rheology, to their hydrolysis products, to processes for preparing them, and to the use thereof.
2. Description of the Related Art
Solid resins of vinyl ester polymers or in particular of vinyl ester-ethylene copolymers have a frequent tendency toward blocking. It is known from EP-A 959114 that the surface tackiness of vinyl ester-ethylene copolymers can be reduced by copolymerization with propylene. It is also known that silicones have good release properties; that is, a surface which repels tacky substances. Blends of solid vinyl ester resins with silicones, however, have unsatisfactory properties: owing to the incompatibility of vinyl ester polymer and silicone, phase separation occurs and/or silicone domains develop, and hence the solid resins become cloudy. The development of silicone domains and the presence of unattached silicone, moreover, lead to migration effects.
From the prior art there are a number of processes known in which organic polymers are modified with silicones by polymerizing the monomers in the presence of a silicone:
EP-A 0352339 describes protective coatings for concrete structures, which comprise copolymers of divinyl-polydimethylsiloxane with acrylate or methacrylate esters and with vinyl- or acryloyl-functional alkoxysilanes in the form of a solution in organic solvents. Heat-curable acrylic resin solutions in organic solvents, which are used for coatings on metals, especially stainless steel, are subject matter of EP-A 159894: in order to improve the metal adhesion, in particular for the purpose of preventing flaking of the coating on deformation of the coated metal parts, acrylic resin solutions are used, of copolymers formed from (meth)acrylate, hydroxy- or epoxy-functional (meth)acrylate, vinyl-functional polysiloxane, and vinyl-functional silane. For improving the adhesion the polymers are postcrosslinked using organotin compounds as crosslinking catalysts, and are cured thermally.
EP-B 771826 describes aqueous binders for coatings and adhesives which are based on emulsion polymers of vinyl esters, acrylic or methacrylic esters or vinylaromatics and which, as crosslinkers, comprise polysiloxanes having unsaturated radicals, examples being vinyl, acryloyloxy and/or methacryloyloxy groups. In this case the organic monomer is emulsified and polymerized and after a certain point in time, during the reaction, the silicone is added. Additives which can be added subsequently include polymerizable or nonpolymerizable silanes of low molecular mass which allow further, subsequent crosslinking of the polymer with organotin compounds.
EP-A 943634 describes aqueous latices for use as coating materials, which are prepared by copolymerizing ethylenically unsaturated monomers in the presence of a silicone resin containing silanol groups. Inter-penetrating networks (IPNs) are formed between the polymer chains and polysiloxane chains. EP-A 1095953 describes silicone-grafted vinyl copolymers, where a carbosiloxane dendrimer is grafted on the vinyl polymer.
The use of vinyl-functionalized silicones is likewise known in the prior art. Generally, the vinyl silicones are reacted with H-silicones (organic hydropoly-siloxanes) in a hydrosilylation reaction by means of a catalyst (usually a Pt compound), such reaction being described, for example, in EP-A 545591. U.S. Pat. No. 4,987,180 describes the emulsion polymerization of a free-radically polymerizable silicone which contains, for example, mercapto, vinyl or methacryloyloxypropyl groups along the chain and is in the form of an emulsion in water with acrylic and/or methacrylic esters, where up to 10% by weight of the (meth)acrylate monomer may be replaced by further functionalized monomers, such as glycidyl methacrylate (GMA), N-methylolacrylamide (NMA) or acrylic acid, and up to 20% by weight of the (meth)acrylic monomer may be replaced by further monomers, such as styrene or vinyl acetate. The emulsion may further be admixed with H-silicones and subsequently crosslinked further with a catalyst.
Polysiloxane-crosslinked styrene-butadiene copolymers are known from U.S. Pat. No. 5,086,141, the crosslinked copolymers being prepared by the suspension polymerization process. U.S. Pat. No. 5,468,477 relates to vinylsiloxane polymers prepared by polymerization in the presence of mercapto-functional silicone.
DE-A 10064092 relates to polyorganosiloxanes for producing abhesive coatings which cure without introduction of thermal energy or radiation. These are silicone block copolymers composed of a crosslinkable hard segment polymer component and a soft segment polyorganosiloxane component. These silicone block copolymers are prepared by a coupling reaction of the block segments or by polymerization of the hard segment component in the presence of polyorganosiloxane.
The products obtainable with these processes, however, fail to satisfy in respect of transparency, migration, and melting behavior. The object was therefore to provide a solid vinyl ester resin distinguished by high transparency, little or no migration, and advantageous melt rheology, and, consequently, by excellent thermoplastic processing properties.